Messages in this thread | | | Date | Mon, 24 Mar 2008 18:38:56 +0100 | From | Jörn Engel <> | Subject | Re: [PATCH] 3/3 maple: update bus driver to support Dreamcast VMU |
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On Mon, 24 March 2008 18:07:07 +0100, Jörn Engel wrote: > > The second rearranges the list locking a bit. Previously it was > possible to touch maple_waitq or maple_sentq without holding the lock. > With my limited understanding of the driver, the second patch may > already be enough to prevent the type of corruption you've been seeing.
Limited understanding indeed. The problem in the mtd driver is that it has no concept of ownership. For example maple_vmu_read_block() does the following: mdev->mq->sendbuf = sendbuf; ... maple_add_packet(mdev->mq);
It accesses some field in mdev->mq, then sends the structure off to maple_add_packet(). From this point on, mdev->mq belongs to the bus driver - until it calls the callback, vmu_blockread() in this case.
But a second thread can call into maple_vmu_read_block() again and access mdev->mq while it rightfully belongs to the bus driver. Bad things will happen.
So these two patches try to close the race windows. Please note the FIXME in the write patch - I didn't do all the work. Real life calls for attention, so these will be the last patches for a while.
Jörn
-- The only good bug is a dead bug. -- Starship Troopers
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